摘要:

A new model of collisionless drift‐wave turbulence fork⊥ai≪1 is explored that can explain the experimentally observed spectra in a simple way. The model includes clumps on an equal footing with drift waves. The calculation is approximate but does confirm the feasibility of the model and demonstrates that clumps are likely to be an important feature of drift‐wave‐related turbulence.

ISSN:0031-9171    

DOI:10.1063/1.862286

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The intensity dependence of inverse bremsstrahlung due to the oscillating velocity of electrons in a laser field can severely degrade collisional absorption efficiency. Previous work has concentrated on the classical and quantum expressions for the absorption rate. Total absorption requires evaluation of such expressions in the inhomogeneous field structure within the plasma, however. Both analytic and numerical calculations to determine the magnitude of the fractional reduction in absorption have been undertaken for the realistic case of an inhomogeneous standing wave. A simple physical model is derived and extrapolated to Airy‐like field distributions. Numerical calculations employing fluid simulations with a heuristic intensity dependence were found to be in excellent agreement with an analytic model.

ISSN:0031-9171    

DOI:10.1063/1.862287

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A convection instability characteristic of plasmas in an inhomogeneous azimuthal magnetic field is treated in the linear stage and in nonlinear saturation. The analysis is done in such a way that collisional and collisionless limits can be taken, and these limits are displayed along with the more general intermediate result. The instability, known previously in the literature in its collision‐dominated form, is shown to be a ’’flute’’ instability with collisional modifications to the growth rate. The nonlinear saturation is analyzed by examining a finite amplitude restoring‐force term in the differential equation that describes the instability. This term is due to the fact that the instability convects plasma into striations of the plasma column surface, modifying the density gradient driving force. The effects of finite ion gyroradius are displayed, and applications of this study to convection cells in a thermal plasma and to exploding wire plasmas are discussed.

ISSN:0031-9171    

DOI:10.1063/1.862297

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is shown that when an intense, focused laser beam interacts with a dense plasma, relativistic effects may lead to observable synchrotron‐like x‐ray emission. For currently achievable Nd:glass laser intensities, the detectability of 10 keV x rays is expected to be enhanced by anisotropy of the source and by strong polarization.

ISSN:0031-9171    

DOI:10.1063/1.862298

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Density gradients and magnetic fields transverse to the propagation direction can produce polarization dependent phase shifts in a laser probing beam used for Faraday rotation studies of longitudinal magnetic fields in plasmas. The resulting depolarization should be considered when probing with fast optics near the critical density.

ISSN:0031-9171    

DOI:10.1063/1.862299

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The axisymmetric stability of tokamak equilibria with arbitrary cross section is studied numerically using the energy principle. The contribution to &dgr;Wfrom the plasma region is minimized analytically with respect to displacements in the toroidal and poloidal directions. the formulation of Lu¨st and Martensen is used for the vacuum contribution. Bessel–Fourier and other sets of trial functions are then employed to cast the minimization of &dgr;Winto a matrix eigenvalue problem. A computer code namedaxisymevaluates these matrix elements and solves for the eigenvalues. The code is fully toroidal and compressible mode trial functions are included. Wall stabilization is studied by placing a conducting wall around the vacuum region.

ISSN:0031-9171    

DOI:10.1063/1.862300

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A self‐consistent electromagnetic theory is presented, for arbitrary &bgr;, of the flute‐interchange mode of a hot‐electron plasma where the hot‐electron guiding‐center drift frequency may be comparable to or larger than the ion‐cyclotron frequency. In the presence of bad curvature, an interchange instability exists at small and large precessional frequency, and this instability is stabilized by cold electrons. Electromagnetic theory introduces finite‐&bgr; corrections that only modify the results of a simple electrostatic theory that includes only the external drifts.

ISSN:0031-9171    

DOI:10.1063/1.862301

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The growth rate of ion‐cyclotron waves, parametrically excited by a pump magnetic field oscillating in time in a hot plasma, is calculated. The process occurs through the excitation of a slow ion‐cyclotron wave and a fast wave propagating in opposite directions along the magnetic field, as has been found previously for the case of a cold plasma. The growth rate of the waves is found to vanish at a critical temperature, that temperature being higher for a lower value of the ratio of the pump frequency to the ion‐cyclotron frequency. Below the critical temperature the growth rate is always less than the cold plasma growth rate.

ISSN:0031-9171    

DOI:10.1063/1.862302

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The enhancement of low frequency oscillations by lower hybrid waves at electric fields lower than the thresholds of other parametric decay processes is presented. The frequencies and wavelengths of these oscillations agree with the collisional drift wave dispersion relation. The enhancement is localized deep inside the plasma density gradient. The excited drift waves change the density profile and the lower hybrid wave trajectory.

ISSN:0031-9171    

DOI:10.1063/1.862303

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Low frequency fluctuations in the JFT‐2 tokamak are investigated. The fluctuations propagate in the direction of the electron diamagnetic drift velocity and have a toroidal mode numbern=1. Density fluctuations reveal that them=2 mode is dominant; on the other hand, magnetic field fluctuations show a poloidal mode numberm=3. The apparent discrepancy is explained by a sum ofm=2,m=3, and/orm=4 modes. Theoretical analysis based on the magnetohydrodynamic theory of kink and tearing modes agrees well with experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.862304

出版商:AIP    

年代:1978

数据来源: AIP